Yearlings
Osteochondrosis Dissecans (OCD) – Prevention Research
Osteochondrosis Dissecans (OCD or bone cartilage disease) is close to the horse industry’s heart, and the recent increase in X-rays of thoroughbred yearlings has put this issue firmly in the national spotlight. The truth is, no breed of horse is exempt from OCD, since it affects all breeds of horse.
“We still do not know if it is a genetic problem or a dietary problem,” says Dr David Pascoe. “There has also been an increase in the export and import of performance horses such as showjumpers, three day eventers and polo ponies (all requiring x-rays) and OCD is now known to affect all breeds of horses.”
“Although it is not specific to any single breed, it appears that it is more prevalent within warm bloods because they are a bigger and faster growing breed. Despite this, any breed of foal that goes through a huge growth spurt within 2 to 4 months of age is more likely to be affected by this ailment.” David also says that, “another possible cause is the propensity to overfeed which in turn, could cause the huge growth spurt in the formative months of the foal”.
Some interesting work is being done in this field by Ms.Kao Castle, a qualified genetic researcher, based in Sydney. Her specialty is computer analysis, and prior to starting research on OCD, she worked with examining human genetics, DNA and protein segments.
Changing her focus to horses happened rather unexpectedly. She has always been interested in animals and while she was at high school, she actually considered a career in veterinary science. It was only recently – when she was talking to a number of horse breeders and trainers – that she realised not much is known about OCD and yet, there is growing concern about the number of OCD cases in horses. Kao decided that, with her background in genetics and her basic interest in animals, she could probably combine the two and possibly delve into the complexities associated with OCD.
Kao will need to research over one thousand horses to get a true result – a number that is required statistically. Although a great deal of clinical research has been done by professionals in this field, Kao feels that, combined with her genetic knowledge, more answers could be forthcoming. Although a daunting task, Kao has been encouraged by responses from a number of thoroughbred studs in Eastern Australia who have realised that by participating in this research, they will be helping the industry, as well as themselves.
Finding the root cause of OCD will unlock opportunities to find both new treatments and ways to prevent OCD from occurring. “Interestingly, in warm bloods, it has already been discovered that a specific group of genes has differences within it that are linked to having some horses more at risk of contracting the disease”. Unfortunately,” she says with a wry smile, “it is a very large group of genes. However, it does narrow the odds from the 30,000 or so genes in total that makes up a horse’s DNA”.
“It also raises the question again that OCD could be related to rapid growth, as it is specifically to do with cartilage and bone growth. The most fascinating thing is that there are no other real side effects. It would appear that OCD, whether brought about by trauma, sudden bone growth or whether it is inherent genetically, only effects bone cartilage within a specific area”.
Kao is interested to know such questions as: “Why does it not affect the heart? How can it affect only the one growth tissue but not have an impact anywhere else in the horse’s body?” Kao has undertaken this research as she would like it to be useful to the Australian horse industry and hopefully, if she is successful, “the effect will be felt worldwide as well”.
Some Notes on Yearlings
by Dr Jennifer Stewart – BVSc BSc PhD Dip BEP MRCVS
The racing industry is plagued by a high incidence of bone disorders. The serendipitous nature of these conditions necessitates that close attention be paid to diet and exercise. A balancing act between economics, management and nutritional requirements occurs between weaning and 2 years of age – but it is often less expensive to feed a balanced diet than to add supplements.
Protein and amino acids: Horses require a number of grams of protein each day, not a percentage. A feed may be 14% protein, but if the amino acid profile is not correct, it may be only 5% useable. Muscle and bone protein building is so specific that even if the diet provides adequate levels of 9 of the 10 essential amino acids, but only 50% of the 10th, protein synthesis will be reduced by 50%. In addition, if even one amino acid is deficient, the others cannot be used and are stored as fat. Diets unbalanced for amino acids are associated with too much cover and not enough height and muscle.
Athletic ability is determined by genetics, nutrition and training. But while genetics determines the ultimate limit to performance, nutrition and training determine how closely the horse approaches that limit. Even the best and most careful management will not prevent all musculoskeletal abnormalities in yearlings, but micro-management and attention to detail during critical growth periods can help reduce the incidence and severity of problems.